A century ago, when the terms were still current, in most industrialized economies «money proper»
consisted of
gold coins, while
paper banknotes and demand deposits that were redeemable in
gold were mere money substitutes.
The thin - film cell
consists of layers of silver and
gold between the semiconductor layers, but the combined thickness is still only a few hundred nanometers thick, compared to a piece of
paper which is 100,000 nanometers thick.